ΔE 16.9, loose: different enough that you should pick on purpose. Russ. AF Light Blue is much more saturated than Bright Neutral Grey.
Can I use Russ. AF Light Blue instead of Bright Neutral Grey?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Russ. AF Light Blue is much more saturated than Bright Neutral Grey.
Can I use Bright Neutral Grey instead of Russ. AF Light Blue?
The same difference applies the other way round: Bright Neutral Grey is much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.