Some confusion has developed between these terms over the years.
True, and this article isn't helping.
Traditionally High Availability (HA) has meant the same as it does today, ensuring that a localised fault such as a server or network outage, or a disk crash, is automatically handled in such a way that a service remains available, or is restored very rapidly.
Disaster Recovery (DR), as the name implies, is a solution to a more widespread outage, perhaps a fire or a flood, which takes a whole datacentre off-air. It may not be automated, and recovery times are often somewhat longer, especially when it is integrated as part of a general Business Continuity plan which covers more than just the IT aspects of a disaster.
I would say that there is much more confusion between the terms Fault Tolerant (FT) and Highly Available (HA), which may be what this article is really considering.