Biden is a conservative compared to leaders of some European countries...

You can argue for a Faulty Comparison in that the U.S. is not Finland; however, it might be a tough sell. I actually think it is a good comparison. Maybe a Definist Fallacy here on how conservative is being defined. The best response would be pointing out the flaws through example and using the Reductio ad Absurdum (or more accurately, the Reductio ad Consequentia). Mike has a good example about Biden being too Liberal in Saudi Arabia.

You: "So you are saying Biden is conservative because he would be conservative in a country like Finland. Doesn't that mean that he is also an extreme progressive liberal because he would be an extreme progressive liberal in Saudi Arabia?"

Them: "I guess."

You: "If you want to extend the political spectrum to politicians outside the United States we can do that, but we can't just choose the most liberal ones, otherwise that is Cherry Picking and a Biased Sample Fallacy ."

Original Post:

I would say that it's the fallacy of equivocation. The word "conservative" would have different meanings if we're comparing policies from other countries vs the ones in the US. 

Here's an analogy:

Elsa: Timmy is very slow (not fast enough). 

Noah: But he made good timing and would beat your average competitor.

Elsa: Timmy always loses in his team (not fast enough in Finland).

Noah: But his team has the fastest people in the world (Finland is pretty fast). 

A strong argument for Biden being a conservative would be to say that the political spectrum moved right and Finland is just used as a comparison for what the United States used to be; which is what I think the arguer meant to say. 

Added:

After reading the comments, it could also be the definist fallacy. The important distinction would be that a definist fallacy would point to bias, but equivocation would point to poor communication.

Depending on how you define conservative, one could indisputably say Biden is a conservative compared to Maduro.  Or, depending on how you define liberal, that Trump is a left winger compared to the leaders of Iran.  So what?  Like many of the arguments proposed on this website, it falls into the Humpty Dumpty category of fallacy, i.e.,  

“When I use a word,’ Humpty Dumpty said in rather a scornful tone, ‘it means just what I choose it to mean — neither more nor less.’

’The question is,’ said Alice, ‘whether you can make words mean so many different things.’

’The question is,’ said Humpty Dumpty, ‘which is to be master — that’s all.” 

That China calls itself the People's Republic does not mean it is a democracy.  Without a universally accepted definition, words like conservative are ambiguous.  When Elizabeth Warren calls herself a "capitalist to my bones," (and follows it with a plan to forgive all student debt), she means something quite different than what I think a capitalist is.

Biden is a conservative compared to leaders of some European countries...

I think the statement is just an opinion.

Jacob's extended recounting of their expanded discussion may reveal an attempt to convince Jacob using the statement, and I agree it's a non-sequitur/irrelevant point.  It may even be true.  It's just irrelevant.

Maybe black and white fallacy?

He can be anywhere on the political spectrum depending on your point of view.

If your friends were from Saudi Arabia instead of Finland they would say he's too liberal.