They just added the language without definition. It is an assumption, but given Private Investigator licensing is handled by the states, that their definition would be the basis of the definition. Doesnt really matter much, the same definition is adopted by nearly every state, almost verbatim (I personally havent checked every state but at least 20 of them are the same):

“Investigator” means a person who is a licensed investigator under ORS 703.430 (Issuance of license) and who engages in the business of obtaining or furnishing, or who solicits or accepts employment to obtain or furnish, information about:

(a)Crimes or wrongs done or threatened against the United States or any state or territory of the United States;

(b)The identity, habits, conduct, business, occupation, honesty, integrity, credibility, knowledge, trustworthiness, efficiency, loyalty, activities, movements, whereabouts, affiliations, associations, transactions, acts, reputation or character of any person;

(c)The location, disposition or recovery of lost or stolen property;

(d)The cause of or responsibility for fires, libels, losses, accidents, damages or injuries to persons or property; or

(e)Evidence to be used before any court, board, officer, referee, arbitrator or investigation committee. [1997 c.870 §1; 2001 c.838 §1; 2005 c.613 §9]" {Source ORS 703.401.

There are three states that have taken it further (Arizona, Florida and Colorado) and including the additional language relating to Evidence and Experts (see 17(g)).

"(17)“Private investigation” means the investigation by a person or persons for the purpose of obtaining information with reference to any of the following matters:
(a)Crime or wrongs done or threatened against the United States or any state or territory of the United States, when operating under express written authority of the governmental official responsible for authorizing such investigation.
(b)The identity, habits, conduct, movements, whereabouts, affiliations, associations, transactions, reputation, or character of any society, person, or group of persons.
(c)The credibility of witnesses or other persons.
(d)The whereabouts of missing persons, owners of unclaimed property or escheated property, or heirs to estates.
(e)The location or recovery of lost or stolen property.
(f)The causes and origin of, or responsibility for, fires, libels, slanders, losses, accidents, damage, or injuries to real or personal property.
(g)The business of securing evidence to be used before investigating committees or boards of award or arbitration or in the trial of civil or criminal cases and the preparation therefor." {Source: FRS 493.6101}

It was learned through firsthand discussions and IASIR (International Association Security and Investigative Regulators) publications that it is the position of Arizona and Florida that any expert (even retained by an attorney) must be licensed in the state (as a PI, PE, Adjuster, etc) or they can face potential civil and criminal charges.

Personally, I think those requirements wouldnt stand a legal challenge to them in court and may be struct down but until them that is what the statutes say.

Chris