It might also be instinct. I know every time I spar with someone, I touch gloves with them before I begin, be it mma, kickboxing, boxing, muay thai, etc. Always. Between rounds, between breaks, pauses, new sparring partners, everything. And from what I've noticed, most people do the same when they spar. So a lot of the touching gloves might just be instinct after all those months of training and touching gloves before every sparring session.