The Brazil midfielder made a late move to the west London side, with Mauricio Pochettino admitting afterwards that he needed to reduce his squad size.
Sandro himself, meanwhile, attributed the switch to the fact that he could not turn down the opportunity to work with Redknapp once again.
But the Rs boss says he is 'surprised' Tottenham sold the midfielder - especially considering they rejected a bigger bid for the Brazilian from Zenit earlier in the transfer window.
"I was surprised we were able to get him to be honest and that he wasn't playing more," Redknapp told reporters.
"I think Tottenham turned down a big bid from Zenit just before the start of the season. It was certainly four or five million more than we paid for him.
"So I couldn't be more pleased to have him, he's a great character, a good lad and I think he'll be a great player for QPR."
QPR host Stoke City at the weekend in a bid to register only their second Premier League win of the season, their first coming at home against Sunderland.
For Spurs, Europa League action awaits tonight before they host West Brom on Sunday.