Text from deceased relative

My MIL died a few months ago; yesterday afternoon, my husband received a text from his mom’s number, as a follow up to an old 2019 text conversation, saying “I love you”.

We have her old phone with us and we checked it - there’s no trace of said message in her “sent” folder. If we try to call her phone number it goes straight to voicemail.

What could this be - any logical explanation or is this something paranormal?