In some grounds home and away fans may share a stand. Therefore a portion of the seats my be taken up by dividers between fans, such as though the use of netting or lines of stewards between fans. Therefore, in a "normal" game where the standard allocations apply some seats would be lost to this.
In other situations, based on health/safety rules or club decisions about reducing maintenance/overheads clubs may not open parts of grounds during normal matches.
With no mention of any seats, then yes it would presumably be a standing only stadium.