I suspect this was his real motive for travel to PI, not to "learn bomb making."
Bomb making could better be learned here in the U.S.
He probably acquired some EOD experience in the military as well as that contained in the book(s) McVeigh sold, and various FM/TMs easily found at gun shows, mail order catalog, or off the net.
Of course he may have "specialized" in some aspect of this field while in Phil.