Apparently not.
Country Rules and Regulations according LIDO:
WAKE TURBULENCE SEPARATION
B757 and B737-800 when leading ACFT are considered as H.
Ok, I was wrong about it being a mistake by ATC or the authorities, but it doesn't make sense that a 738 is considered H, while the 739 isn't.
It doens't make much sense to me that a 738 is considered H in the first place.
However, doing some PPRune research, I was able to find this:
http://www.pprune.org/atc-issues/202...-category.html
But, it only applies to ATR, Dash-8 and similar aircraft.