The memory that plays is entirely devoid of context. Strange smiles at Arabella who runs up to him, entirely relieved, and gives him a hug. It's definitely something that probably should be private, based on how happy memory-Strange looks and how absolutely relieved memory-Arabella looks.

And then, in the dead center of the summoning circle, Strange appears. He's distracted by the memory for a second, eyes unsurprisingly drawn to Arabella before he puts two and two together and realizes he has no idea how the hell he got here in the first place.

It's like a switch flips in his brain from 'dopey husband' to 'battlefield ready.' Strange tenses up, not saying anything but obviously ready for a fight, as he summons a fireball to his hand and his eyes dart around the room as he tries to get his bearings and take in the situation.