"T" for 4 players?

[Terrapins Fan]

I was at a play off game last night and in the 2nd quarter there wasa time out with under 1 minute to go.

When the players returned to the floor, the home team only sent 4 out by mistake. The ball was put into play and 3 seconds later, the lead noticed that the home team only had 4 players on the floor and stopped the game. Visitors were up by 2 at this point. The officials come together and a "T" is called.

When the official stopped the game, the home coach noticed that he only had 4 players on the floor and sent his 5th player to the table to check in.

What was the "T" called for? A player delaying coming on to the floor?

Should it have been called? Should the game have been stopped?