LIHKG is not pronounced as LIHKG or LI'HKG' or LI'H'K'G'
Linden (lin' dang') is the only pronunciation used by Hongkongers
But why Linden? I don't know, but
Lin is the surname of the app developer of LIHKG
den (pronounced as dang) is the surname for a series of clones all tracing their origins from
hkgolden.com (pronounced as Go' Dang') that explains the "den" part
So we have Xden Yden Zden...etc. in Hong Kong just like Linden.