The French forward scored two goals with two touches to send Arsenal on their way to victory at the Stadium of Light.
Speaking on Sky Sports after the game, Henry said: “When he came on I thought he was going to score. You have to give Kieran Gibbs a lot of credit because he picked him out [for the first goal]. Olivier Giroud is very humble. It is a great assist and a great finish.
“The second goal is all him, Mesut Ozil takes a good corner but he has no right to score from there.
“You have to give him his credit. He’s been injured and people sometimes doubt him.”
Alexis Sanchez gave Arsenal the lead early on when he headed home Alex Oxlade-Chamberlain’s cross in expert fashion.
However, the Gunners were pegged back after the break when Jermain Defoe converted his penalty after Petr Cech brought down Duncan Watmore in the box.
But the Black Cats were not level for long, because substitute Giroud quickly fired home, before adding his second of the afternoon with a header.
And Sanchez then converted from close range to make it 4-1 and send Arsenal to the top of the Premier League table.
Arsenal now turn their attentions towards their Champions League clash against Ludogorets on Tuesday night.
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