They're asking to check his brain for signs of CTE. TYPICALLY, when I have heard this requested, it is in conjunction with a suicide. In my mind, this moves the suicide conjecture closer to probably true.
SPECULATION: He decided to go out on his own terms. Does an act of charity as one of the last things he does before saying goodbye. Killing himself at his friend's house ensures he is found quickly enough that a check of his brain for CTE is possible.
ON THE NATURE OF SPECULATION: Obviously, we're all armchair quarterbacking. Unlike some commentators, I would never ask anyone to treat my speculation as truth. I rush to no judgement and make no proclamations.