Yes, the sentence is grammatically correct.
The meaning of the sentence seems to express surprise or disbelief about a potential connection between the man's question (whether the speaker is the last born) and some underlying reason or situation that the speaker is worried about. The use of emojis suggests a lighthearted or humorous tone.
Here are a few possible rephrasings:
1. "Please don’t tell me that this is why he asked me yesterday if