Yep, that's what he means (though as with NTSC=525, some of those lines were used for sync pulses, subtitles, etc, so the actual resolution was a bit less: 377 lines for a 405 line picture. And, to add to the complications, the film telerecordings could only record every other line, so they were only 189-lines. Fortunately every Who episode up til then was re-recorded when an 377-line improved technique was developed in '67, but a few surviving episodes recovered from overseas only exist as the earlier 190-line versions).
So, every episode up until Enemy of the World 2 was made on 405-line video, usually on 2" Quad VT (though about 10 1960s episodes were transferred to film before transmission, either so they could be edited more easily, or just because there wasn't a VT machine available).
Enemy of the World 3 through to War Games 10 were made in the colour-compatible 625-PAL format, but only in black and white. After the all film one-off of Spearhead from Space at the start of season 7 (a strike cancelled the studio scenes, so they were shot on film on location to get round this), the rest of the original run was made in 625-line colour PAL. From Seasons 7 to 19 they were recorded onto 2" tapes, then the new 1" format took over as of Arc of Infinity.
All the surviving tapes from seasons 7 to 19 were given to the BFI archive after the BBC made digital archive copies in the 1990s. The 1" tapes were also copied to digital, but haven't been kept.
One possible, but not proven, reason for Enemy of the World 3 surviving is that it was the first 625-line episode: a film copy MAY have been made for BBC bosses to view to see how Doctor WHo looked in 625-line (in theory, you;d think they'd have watched a videotape. But the BBC had a lot more film projectors than VTRs, and the latter would be too busy actually making or broadcasting programmes). The original video tape exists with a 1971 Blue Peter on it (but, as mentioned, that would be an early 625 line tape, not a 405-line one. Though the tapes are identical, just used for a different format).
A reason for the absence of tapes dating back to the 405-line days MAY be that the licence fee for a colour-capable 625 line TV was about four times as much as the old Black and white licence. That meant the BBC got a real boost to its income as people converted, which MAY have let them buy new tapes and bin the 10 year old ones that were falling apart...