The title-chasing Tigers led 1-0 courtesy of Mallik Wilks' clinical 51st-minute strike and looked to be heading for just their second win in seven League One outings when disaster struck at the KCOM Stadium.
There seemed no danger on the cards when Richie Smallwood rolled the ball back towards Reece Burke near halfway, however the latter's slip allowed Tangerines substitute Ben Woodburn to seize possession and scamper away towards George Long's goal.
The City centre-half did his best to recover and get back into a position where he could attempt to atone for his initial error, only to succeed in hauling the on-loan Liverpool youngster down just outside the home box.
The outcome was inevitable, and not long after referee Samuel Barrott brandished a 77th-minute red card in Burke's direction, Blackpool levelled matters through Jerry Yates' close-range strike at a corner.
"I thought we were in control of everything that we were doing and then there's a moment of madness, which is unlike us, really," McCann said.
"It was a sloppy bit of play in the middle of the pitch. Richie has played it behind Reece, he's tried to recover and then it's a red card.
"It was both of them, they just got caught up in a tangle, didn't they. There was no-one near them. It was just a casual pass from Richie and it's put Reece on the back foot.
"To be fair to him, he's actually recovered quite well and got back. We thought he was going to nick the ball but it wasn't to be, but even though Reece got sent off we shouldn't have conceded the way we did from a corner."
A man down though they were at the time, McCann is adamant that the players who were on the pitch should still have been able to prevent the Tangerines drawing level in the fashion they did.
"It's frustrating for us because they've had one shot on target, it's come from our own doing and from someone leaving their man in the box. It ends up in the back of our net and we have to learn from it," he added.
"We shouldn't concede from the corner. It's really, really disappointing, poor from us. We have to learn from that, it's a cheap goal to concede.
"We shouldn't concede that goal with eight or nine men on the pitch, never mind 10, so we are frustrated with that one."
Saturday's result keeps Hull second in the table, but they now sit three points behind leaders Lincoln having played the same number of matches.