That's interesting. I started with 2E, and the both times in recent years I tried gaming in 1e games they insisted on 'playing it by the book' and rolling 3d6 in order.
It did feel like a tedious and masochistic exercise both times.
That's actually not really...by the book either (unless one ignores the advice specifically given on characters rolled with 3d6 only prior to the Methods given for rolling characters).
He suggests instead the following as four alternatives for player characters...
The Default, or Method I is
All scores are recorded and arranged in the order the player desires. 4d6 are rolled, and the lowest die (or one of the lower) is discarded.
Method 2 has all scores being rolled and arranged as Method 1 but 3d6 are rolled 12 times and the highest 6 are used.
Method 3, has it so that each ability score is rolled in order with 3d6, but you roll 6 times for each ability score and keep the highest out of the six rolls for each score
Method IV has 3d6 rolled to generate 6 ability scores in order for 12 (yes, that's TWELVE) characters and then you select whichever one you want.
None of them were roll 3d6 in order ironically as the generating method. (I should add that he does mention to generate playable characters by rolling 3d6 it is a little discouraged and indicated they are marginal and tend to have short life expectancy). When the PHB came out I suppose one could have used the OD&D method (if they were old enough to even have been playing that, but I find most people were not part of that crowd), but technically the methods to rolling came later in the DMG (page 11 of the reprints). With OD&D later on, there were various ways of generating Ability scores so...not really buying that they were from that era of gaming.
More normally those who play it that way got their start with either BECMI or BX and kept generating scores with those methods rather than what was suggested in the AD&D books from what I gather (the 3d6 in order method).
In generating ability scores the AD&D PHB actually references the DMG as telling what methods should be used to generate ability scores.
HOWEVER...as Gygax basically said the books were more like...guidelines...anything could be by the book...but 3d6 rolled in order wasn't really one that was suggested for AD&D. (He did go over a bell curve of 3d6 on pages 9-10 however).