I can't be 100% sure.
The only other thing (and I'm not sure it's even possible either) but maybe there was a small amount of hcg left in my system and this is a new pregnancy which has added to the existing hcg making it possible for the hpt to pick up the BFP early? Again, I'm probably being hopeful rather than realistic.
I did another test with Fmu and the line is very faintly there again. I guess now I'll need to wait at least till 10dpo and see if it's darker then see my GP. I already have my follow up appointment from the recent loss booked with ob so if it's positive at least I won't need to wait for an appointment Lo..