Deliberate mistake: The whole Monaco race sequence is totally (but deliberately) ludicrous. First no driver would be allowed without a fireproof mask and rest of required security measures, as Stark does. Second, the real-life security controls are very strict: When an accident occurs a safety car shows up, flags and audio advices signal the racing cars for them to lower their speed and avoid accidents. Nothing to do with the wild, uncontrolled race depicted here.
Deliberate mistake: Whiplash's Orange jumpsuit defies physics. The scene shows Whiplash powering up his harness at the race track, which burns off the top section of the jumpsuit, however the jumpsuit then mysteriously and impossibly appears tucked under the harness's belt. If the belt was in the inside of the jumpsuit, the jumpsuit would just fall to the ground and leave Whiplash basically naked, and not be tucked under the belt. If the Harness belt was placed on the outside of the jumpsuit, then the remains of the jumpsuit would have draped over the belt covering it up. There is no way the jumpsuit can end up tucked under the belt, but its done so Mr. Rourke and the movie can remain PG.
Answer: He wanted to do something nice for her, but since he is a pretty self-absorbed, shallow multi-billionaire, he forgot about her allergy. He remembered that there was SOMETHING about her and strawberries, but misremembered and thought it meant she really liked them. He makes a simple human mistake, not out of meanness or spite, but because he honestly does not remember.