Ichiro said it in a vaguely hurt way, but years of friendship with the guy told me it was a total lie.
Literal
Ichiro [topic-は] vaguely hurt-[appearance-ように] said [but-が], that [subject-が] total-lie [copula-である] [nominalizer-こと] [topic-は] this-guy [with-との] many-years [possessive-の] association [subject-が] taught-[benefactive-くれた].
どことなく ('vaguely, without being able to pinpoint it') is an adverb for an impression you can sense but can't specify. 嘘っぱち ('total lie, complete fabrication') is an emphatic slang form of 嘘, with っぱち as a derisive suffix. こいつとの長年の付き合いが教えてくれた personifies the friendship — 'the relationship itself taught me' — a warm way to express intuitive knowledge born from closeness.