First off, it's 50% of the vested account balance - that's an important distinction.
Second, as Bri points out, it's not correct in the event there are other loans. Even if the plan only allows a single loan at a time, the $50,000 limit is still reduced by the highest outstanding loan balance in the past year. If you wanted your language to apply, the plan would need to say that a participant may only have one outstanding loan at a time, and also that they may not take another loan until at least 1 year after the final repayment of the previous loan has been made.