> There was no 1Password to LastPass importer at the time I wrote that
The details were hazy, but in 2016, there was a way to export your passwords from LastPass and import them into 1Password, though I don't think there was a way to do so on windows (which I believe is what your importer addresses).
After LastPass vulnerability in July 2016, I switched to 1Password.
Password managers generally use CSV, avoiding vendor lock-in. However, back when Lastpass doubled their subscription cost (yes, doubled, literally) I switched to Bitwarden. At that point, there was some issue with exporting passwords with a certain character (IIRC it was ; or #). I ended up changing the few passwords which quit working.
As for OP, my take is you clicked a bad link triggering a zero day vulnerability in your browser, or perhaps you logged in on Lastpass via a VPN or Tor? Its pure speculation though.
The details were hazy, but in 2016, there was a way to export your passwords from LastPass and import them into 1Password, though I don't think there was a way to do so on windows (which I believe is what your importer addresses).
After LastPass vulnerability in July 2016, I switched to 1Password.