callable convertibles

Hello,

on question 24 of the reading 47, the curriculum suggests that if a convertible gets called by the issuer, you are forced to convert into shares. Isn’t that a mandatory convertible (so with 2 strikes) ?

I thought the call option on a convertible was an option on interest rates (if rates go lower, the issuer has the right to call the bond back, e.g., pay you CASH and not stock)

So why would you be forced to convert in that case ?