Not exactly, but it could be clearer that is for dry areas only for small format tiles. Dotting and dabbing is not spreading, so that's his argument already out the window regardless.
Initially, part 1 should be followed, but special considerations should be made in specific areas (which the 2009
standards didn't directly apply to), which is when anything in part 4 should be made a priority, until such time that any updates in part 1 match or exceed what part 4 recommends.
So if he was basing it on the 2009 standards, he should also refer to part 4, 2015, which says:
Section 7 - Wet and damp conditions:
7.2.2 Installations in high humidity areas:
Tiles should be solidly bedded in a water-resistant adhesive
7.2.3 Installations not immersed but subject to occasional wetting (reference made to domestic non-power showers)
a) Tiles should be solidly bedded in a water-resistant adhesive
7.2.4 Installations not immersed but subject to frequent wetting (reference made to wet-rooms, domestic power showers etc)
c) The tiles should be solidly bedded so that voids behind them are eliminated as far as possible
And if he doesn't know how to achieve solid bedding, he should revert back to part 1, 2009 to:
7.2.1.5.3 Notched trowelling and buttering method
The notched trowelling and buttering method combines 7.2.1.5.1 and 7.2.5.2 and should be used for large tiles (3.4 (mathematically refers to 60x30 upwards)) and tiles with ribbed, deep keyed or heavy buttoned back profiles. A thin coating of adhesive buttered over the backs should fill the deep keys before placing the tiles in position on the combed adhesive bed. There should be no significant increase in bed thickness.
Note This method aims to achieve a solid bed but, in practice a small number of voids are inevitable. (this doesn't mean a gaping 50% of no contact).
Also as
@acaciaguy says, tanking is also advised under part 4, even before it became part of the 2018 part 1 update:
7.2.3 Note 1
For water sensitive backgrounds e.g. gypsum plaster, additional protection in the waterproof tanking system may be considered
Note 2 The use of impervious grouts and adhesives is no substitute for a tanked installation.