Celtic fans have peddled this myth for years. Souness didn't say anything of the sort. Your point is still valid, it was cringeworthy, but Souness was not guilty. It was Gary Flitcroft who went public with that remark. I know Flitcroft 'claimed' that Souey had said it in the dressing room but he denied even doing that (which actually would have been okay in the privacy of the dressing room anyway). As I recall Souness actually kept a surprisingly low profile during that tie, given his background. Flitty got a bollocking off him as well, for his troubles, by all accounts.
https://www.thescottishsun.co.uk/sport/football/4880340/celtic-rangers-reward-attacking-europe-kris-boyd/