OK, do they put a few millions on the table when they hire the team, with an additional retention bonus for each person of the team?

Otherwise it's nothing like an acquihire.

It's not really the same thing as an acquihire. In an acquihire a company acquires another company and then chooses which employees to give job offers to. In many cases only a handful of top employees are actually hired, the rest are fired. Stripe is saying that it wants to try to hire whole teams.

Acquihires of companies that only have 2-5 members usually involve the entire team.

Well now it's becoming cheaper for them to hire a team.

I don't think this is the same thing. If you want to hire the vast majority of people, it may well be easier to acquire the company. What happens if the other company is much bigger than you though? Stripe would never be able to buy Google, Microsoft, Apple etc., but they could potentially hire a small internal team from them.

Acquihires don't necessarily involve the entire team. I've certainly heard of people who were on the wrong end of "We'd like to buy your company and offer jobs to n-1 of you."