Is it because of the incident?

[Talab1234]

Person 1: We left the office at 8 pm last night.
Person 2 Answer: Is it because of the incident?

Is the answer grammatically correct?

 

[Barque]

Not a teacher

It's grammatical, but I'd expect "Was that because...?" You're referring to something in the past.

Also, "the incident" doesn't sound very natural.

Was that because of the crowd outside?
Was it because the police didn't let you leave earlier?

In actual speech, you'd probably hear a very different structure. "Why [was that]? Didn't the police let you leave earlier?"

 

[Tdol]

Incident is often used to make something sound less serious, but it is less likely to be used in a conversation like this..