Past tense is usually considered significant by the professionals who analyze these kinds of things. I have to say, I’ve never referred to my daughter in the past tense. They’d also only been missing a day at this point, and this was Tuesday, why wouldn’t he think Bella would still start school the next Monday.. surely they’ll be found by then ..
Like someone else mentioned, he was consciously talking about Bella and Celeste in the present tense and then slipped up IMO.
All a bit moot now I guess though, since we all know for sure he was lying. Still, it’s interesting to watch it after the fact.