No one is saying its a bioweapon, merely shoddy containment in a facility that did viral research, the research could have been entirely altruistic, its still their fault for letting it out of the lab and then hiding the fact, arresting doctors and journalists and letting it spread. When they could have been letting other countries take precautions to prepare for it and shut down travel out of the country sooner instead of telling the world there is no real danger, no human to human transmission, and everything is fine.
On the other hand, prefaced with the fact that it isn't one, or was still under research if that, bio-weapons are just as effective when they disrupt an economy and infrastructure and a virus targets the elders or those at an age of those most likely in leadership positions. So it doesn't have to kill military aged people to be effective. Again, this is likely not one, but the disruption its caused and economic hit its taken is in line with how modern wars are fought. They only need to overwhelm medical facilities, its like the case with mines, they don't kill so much as maim, because maiming soldiers puts a greater strain on an army to keep them alive, transport them and treat them (even though they'll never return to the battle field), then if they were simply dead. You kill a soldier, they're down a man, you maim/disable a soldier, they're down a man, two other soldiers needed to evacuate him, they're down transport needed to get them back to a medical center, and several medical personnel needed to treat them and get them stable. You want to cripple an army, you don't kill it, you make it so the soldiers barely survive and need assistance, or you take out their resources, this virus does a good job of both.
A virus only has to severely disable economies and create a strain on resources to be effective at crippling an opponent, if its not especially deadly, it can spread further, if it puts enough soldiers in hospital beds, especially senior leadership, its effective. Even if this isn't a bio-weapon, it actually would be pretty effective as one assuming you already had the vaccine, which no one does.
https://www.youtube.com/watch?v=bpQFCcSI0pU