"Ability to replace calcium in certain biochemical processes" is not nearly the same as "chemically similar to calcium". It's like saying if I stole your login for facebook I would look like you and nobody would be able to distinguish between us without DNA test. Completely different things. Biochemical processes are known for accepting a lot of substitutes, that's how a lot of drugs work. That does not mean all those are chemically similar in general - they just play similar roles in certain processes.