And he revealed the club are ready to appeal Joe Rafferty’s dismissal after reviewing footage in the aftermath of the goalless draw.
Rafferty and Jake Forster-Caskey had a scuffle in the middle of the pitch after the Stevenage man went into a tackle with the right-back on 56 minutes.
As a consequence, referee Simon Mather, helped by his assistants, subsequently showed a red card to both players.
Potentially, Pompey could now lose Rafferty for three matches if it is decided to be violent conduct.
Although Mousinho doesn’t believe either player should have been dismissed.
He told The News: ‘I thought it was a bit bizarre that both of them were sent off – and I think we will appeal.
‘We obviously have to take all of the evidence into account and we usually take the opinion of an ex-referee to see what they say and then go from there. But, from what I have seen, it is worth an appeal.
‘I spoke to Joe after the game and he said that there was absolutely nothing in it. He grabbed the guy's leg and he didn’t really think the Stevenage player kicked out at him. Both players were on the floor and the referee decided to send them off.
‘You can probably tell from the reaction of both players that they were a bit shocked in terms of what happened and didn’t necessarily see it – I don't think anyone did apart from the refereeing unit.
‘It’s a really, really strange one, we’ve watched it back, there’s absolutely nothing in it. We’ve got the angle from the far side, so it will be very interesting to see if there's an angle from the near side to sum up what’s gone on.
‘I don’t think either of them should be sent off, we certainly didn’t have any complaints. The reason we appealed in the first place was because of their challenge, it wasn’t a great one.’
In Rafferty’s absence, the Blues went to a back three, with Abu Kamara and Jack Sparkes initially operating as wing-backs.
However, the fixture ended 0-0, representing the third time in five League One matches this season that they have drawn.
Mousinho added: ‘Speaking to Rafs, who has no reason to lie to me, ultimately he has to come out and admit it because he knows it’s on camera.
‘He says he has done nothing – and, from what I can see, he absolutely hasn’t.’