The two most common architectural metamodels are provided by The Open Group:
Both metamodels are voluminous and consist of 30+ artifacts and 100+ potential relations between artifacts. They provide a maximum that attempts to cover each and every potential usage scenario. Companies typically need to heavily downsize them before implementation, which means that they end up with a proprietary rather than a standard model.
Vendors of enterprise architecture tools typically define their own meta-model, more or less compliant to the standards defined by The Open Group, which can be customized to a company-proprietary model.
So yes, there are standards, but they are so universal and require intense customization, so that it questions their role as a standard.
What is different in Architectural Thinking?
Architectural Thinking consists of a minimum, core set of artifacts that are beyond dispute and exist in any company. This is important, because in Architectural Thinking many business roles implement the architecture. Thus, the model must be simple and self-explanatory otherwise it will not be accepted by a wide range of stakeholders.
Companies are encouraged to extend the core model according to their usage scenarios. Compared to the standards mentioned above, the approach is vice-versa: while existing standards provide a maximum-fits-all approach that must be downsized, Architectural Thinking defines a powerful core that can be extended by companies.
Architectural Thinking defines a lightweight architectural model that wants to be a true standard.