Is this conversation ok?

[jasonlulu_2000]

---Why, the door is still open.
---How come? I’m pretty sure I remembered to lock it.

Is this dialogue natural from a native's point of view?

Thanks!

Jason

 

[5jj]

---Why, the door is still open.
---How come? I’m pretty sure I remembered to lock it.

Is this dialogue natural from a native's point of view?

No. Affirmative statements beginning with why have not been standard for many years.

 

[Raymott]

Also, the second speaker would not say "How come?", because the first speaker obviously doesn't know why.

 

[jasonlulu_2000]

---The door is still open.
---How come? I’m pretty sure I remembered to lock it.

What about this time?

Thanks for your help!

Jason

 

[Raymott]

---The door is still open.
---How come? I’m pretty sure I remembered to lock it.

What about this time?

Thanks for your help!

Jason

Yes, that's more natural.