It’s true that most applications were stream oriented, and Minitel was, as the users’ sessions were only bytes (in videotex encoding) rendered by the Minitel as a serial terminal integrating a modem (1200 bauds reception, 75 bauds emission!).

There was a smart gateway node that translated complex x25 from the Minitel service providers nodes into simple bidirectional stream of bytes to the Minitels, it was a specialized type of packet asssembler disassembled (PAD) called a PAD Videotex (PAVI).

Now x25 did have packets, Minitel terminals did not. So the PAVI and x25 servers were working very differently and with more complexity (hence smart) than Minitel serial terminals (hence dumb).

It’s not that x25 mandated dumb terminals.