If it wasn't like heaven, it probably wasn't.
Well, seriously, if it had a big Star Gold sign in front then that would've been the Premier lounge.

But good news for all Biz class passengers (even the non-SQ/LH ones): You are allowed to access the Silver Kris. Source: Star Employee's Guide.

On a matrix of the lounges that each "category", ie First/Biz/Star Gold, is allowed to access, it mentions that Star Gold (and paid access members) should use the Premier lounge in SIN, but no such mention for First/Biz passegers. It means that other Star airline's First/Biz passengers can use the SQ Silver Kris F/J area respectively!

Can someone try it next time, flying a non-SQ/LH carrier and go into the Silver Kris? It would be interesting to see. If they give you any trouble ask them to refer to the Star Alliance "Products and Services" guide.